An image forming apparatus for recording medical image such as digital radiography system, CT and MR using a regenerative fluorescent sheet employs a wet process which comprises taking a picture or recording an image on a silver salt system photographic material which is then wet-processed to obtain a reproduced image thereon.
In recent years, on the other hand, a dry system recording apparatus requiring no wet processing has been noted. Such a recording apparatus employs a photosensitive and/or heat-sensitive recording material (light- and heat-sensitive recording material) or a heat-developable photosensitive material film (hereinafter referred to as "recording material"). In this dry system recording apparatus, the recording material is irradiated with laser beam (scanning) at an imagewise exposure zone to form a latent image therein. Thereafter, the recording material is allowed to come in contact with a heating means such as heating drum at a heat development zone to undergo heat development. Thereafter, the recording material on which an image has been formed is discharged from the apparatus.
The foregoing dry system can not only provide image formation in a short period of time as compared with the wet system but also can eliminate the necessity for disposal of waste liquid as in the wet system. It can be well expected that there will be growing demand for this dry system.
In the foregoing dry system, particularly for medical use, a multiple gradation image having a high quality is required. Therefore, even a density variation due to a slight variation of exposure on the recording material can be easily recognized as an uneven image.
On the other hand, the imagewise exposure zone employs laser beam as an exposure light source. The laser beam is a coherent light. Therefore, when the laser beam hits the recording material, it is repeatedly reflected by various layers constituting the recording material to cause the generation of interference band in the image thus formed. As an approach for inhibiting the generation of interference band there has been practiced a method which comprises inhibiting interference by destroying the phase of light reflected in the recording material, e.g., by providing a light-scattering layer under the lowermost image-forming layer of the recording material or roughening the surface of the support supporting the image-forming layer. However, such an approach is disadvantageous in that even the light scattered by the light-scattering layer or roughened surface can form a latent image that causes image quality drop.